Unhexhexium
Unhexhexium, Uhh, is the temporary name of element 166. In the periodic table of elements, it is a p-block element and the third last one of the 8th period. As of 2012, no attempt has been made to synthesize this element. It is predicted to be a chalcogen. Properties NUCLEAR At least one set of theoretical values for half-lives and decay modes of Uhh have been constructed for neutron count up to N = 333(3). It predicts isotopes in a band ranging from Uhh 453 to Uhh 484. Examination of pp 15 & 18 of Ref. 3 indicates that Uhh 453 through Uhh 458 have sub-microsecond half-lives and decay by fission. Uhh 459 to Uhh 465 have sub-millisecond half-lives and decay mainly by alpha emission. Uhh 466 to Uhh 475 apparently decay by alpha emission and have half-lives ranging up to around 1 sec. Isotopes between Uhh 476 and Uhh 484 also decay by alpha emission, but have short halflives. These predictions are to be expected for a neutron shell closure at N = 308. Ref. 3 also shows a predicted isotope at Uhh 498, which is probably an artifact. What Ref. 3 can’t do is describe heavy isotopes of Uhh. It is possible to use a first-order, liquid-drop approach to guess at the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. At least two computations of the neutron dripline’s location up to Z = 175 exist(4),(5), and since they give similar results, the maximum possible size of a Uhh nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Uhh 593 as the heaviest possible Uhh isotope. Structural correction required for Uhh 593 itself is around 0.5 MeV, which means all Uhh drops will fission quickly without structural stabilization. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(5),(6), 370(5), 318(7), and 308(3). The isotope Uhh 572 requires a little less than 1.5 MeV of structural correction, which means isotopes in the Uhh 562 to Uhh 577 band are likely. (See “Formation” for additional significance of these nuclei.) Uhh 536 requires around 1.5 MeV of structural correction, which means isotopes in the band Uhh 526 to Uhh 541 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Uhh 484 requires around 2.5 MeV of correction energy, which means alpha-decaying nuclei are likely in the band Uhh 474 to Uhh 489. Ref. 3 does not show a pattern of nuclides which indicate a shell closure at N = 318. ATOMIC Several predictions for the ground state electron structure of Uhh agree that it will have alkaline-earth metal character, with two 9s electrons the main ones available for bonding. It's 7d electrons might also participate. Electrons in Uhh can be described in terms of time-independent orbitals, but calculation of electron properties require that nuclear charge be distributed over the nucleus' actual volume. In addition, there is some chance that differing nuclear shapes may produce different electron configurations in different isotopes. (Different isotopes would be different elements in the chemical sense.) Except in the laboratory, Uhh is expected to exist only in environments too hot for ordinary chemistry to occur. FORMATION Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uhh 561 to Uhh 577 to form in quantity during such a merger. It improbable that nuclides between Uhh 526 and Uhh 541, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uhh 453 to Uhh 484 band. Quantities produced by this method are very small. (12-12-19) References 3. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 4. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 5. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 6. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 7. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. Category:Undiscovered elements Category:Chalcogens Category:Radioactive